Monique's teacher has asked her to add acid to 8 gallons of a 32% acid in water solution to get a solution which is 70% acid. how much pure acid should she add?

Let x represent the number of gallons of acid Monique adds to the mixture. Then the total amount of acid will be ...
  0.32*8 + x = 0.70(8 +x)
  2.56 + x = 5.60 + 0.70x . . . . . simplify
  0.30x = 3.04 . . . . . . . . . . . . . . subtract 0.70x+2.56
  x = 3.04/0.30 = 152/15 = 10 2/15

Monique should add 10 2/15 gallons of pure acid.